There are two ways of changing the .NET pool when you are using Orchard CMS / https://orchardcore.net/
1. If you are using the IIS Remote Manager please follow these steps:
- Open IIS Manager. For information about opening IIS Manager, see Open IIS Manager (IIS 7).
- In the Connections panel, expand the server node and click Application Pools.
- On the Application Pools page, select the application pool that contains the application that you want to change.
- In the Actions panel, click View Applications.
- Select the application whose application pool you want to change and then click Change Application Pool in the Actions panel.
- In the Select Application Pool dialog box, select an application pool from the Application pool list and then click OK.
2. If you are using the WebSite Panel: Log in the WebSite Panel -> Click on WebSites -> Click on the particular website name-> Click on tab
"Extensions" and set the ASP version to 4.0